"...choose you this day whom ye will serve...but as for me and my house, we will serve the LORD." Joshua 24:15

Monday, March 10, 2014

V5.7 - Make sure your Jointer is flat

So, we were talking about our little friend, the
Jointer last week. We went over some of its basics and what it can do. Thinking
maybe this week we’ll just outline some of the ‘care and feeding’ of it.

Like we said, the jointer is just “two flat tables,
with a rotating cutterhead between them”. A simple and not very complicated
machine, but oh so much it can do for you. In order for it to perform at its
best, there are a few things that you need to pay close attention to. One thing
is those tables I mentioned. They need to be nice and flat AND they need to be
nice and flat. I know, that sounds weird, right? Here’s the thing: each table
needs to be nice and flat… and the whole machine needs to be nice and flat
also.

A couple of tools that are a must when making sure
that your jointer is ‘nice and flat’, is a machined steel straight edge and a
set of feeler gauges. The bigger your jointer is, the bigger your steel
straight edge needs to be. A short straight edge can be used to check an
individual table, but to check the whole table surface, the straight edge needs
to be at least three-quarters as long as the whole jointer. In other words, if
your jointer has an overall length of 6 feet, your straight edge ought to be 4
feet long. Here’s why. When checking an individual table, first you would use a
‘ladder pattern’. You’d lay the straight edge on the table surface-just inside
the edge of the table-and use the feeler gauges to determine if the surface is
within the manufacturer’s flatness tolerance. Do one edge and then the other
edge (these are the rails of the ‘ladder’). Then take the straight edge and lay
it across the table in several spaced out places (these are the steps of the
ladder) and check the flatness there.

The last check for an individual table is an X
pattern. This is done just as it sounds. Lay the straight edge from corner to
corner on the table surface and then do the same from the other corner to other
corner. If these flatness checks turn out good, each table is ok.

Then comes the fun part – checking the full
machine. The checks are done the same way, but the straight edge is placed one
the entire jointer surface, after you have raised the infeed table to be level
with the outfeed table.

What this check will tell you is if both tables are
in a proper ‘plane’ with each other. If they are not, your tables may be nice
and flat, but you will never get a successful joint because your board will come
out twisted.